1. Field of the Invention
This invention relates to a tool and method for cutting the protective elements of a monotube optical fiber cable without severing the buffer tube in order to access the buffer tube and the optical fibers found therein.
2. Description of the Prior Art
The use of optical fibers in telephonic and other communication is well-known in the prior art. In order to protect the delicate optical fibers and to facilitate the laying of optical fibers, it is well-known to dispose a number of fibers in a monotube-type optical fiber cable.
In a known cable assembly 10, as shown in FIG. 1, a single large plastic, gel-filled buffer tube 12 can contain approximately 100 optical fibers 14. A similar cable assembly is manufactured by Alcatel Cable Systems which is described in U.S. patent application Ser. No. 07/468,470, filed Jan. 22, 1990 and sold under the designation `Unitube Optical Fiber Cable`, now U.S. Pat. No. 5,029,974. The single centrally elongate buffer tube 12, or "monotube", may be surrounded by water-swellable tape or, as shown in FIG. 1, radial strength yarns 16. The radial strength yarns 16 are made of either aramid or fiberglass materials and are contrahelically stranded around the buffer tube 12 and impregnated with filling compound such as a petroleum-based hot melt filling compound manufactured by Witco Corporation, New York, N.Y., or Amoco Chemical Company, Chicago, Ill. Corrugated steel armor 18 is applied over the radial strength yarns 16. The corrugated armor 18 is flooded with a water-blockable flooding compound such as a hot melt adhesive or a petroleum-based flooding compound. A high strength rip cord 20 is applied under the armor 18 to aid in sheath removal. Two steel strength members 22 are located 180.degree. apart on the outside of the corrugated armor 18. A medium-density polyethylene (MDPE) outer jacket 24 encapsulates the steel strength members 22 and corrugated armor 18 to complete the structure. A water-blockable flooding compound is disposed between the corrugated armor 18 and the outer jacket 24. The cable assembly does not necessarily have to have the corrugated armor 18.
While optical fibers have many advantages over traditional conducting cable in the communications field, such as high density and lack of electromagnetic interference, they have a major disadvantage in that there is degradation in transmission efficiency after a fiber has been spliced or joined with another fiber after the original manufacture. Such a splice may be inevitable in the event of fiber breakage, the rerouting of a communications line or the insertion of an intermediate device within the communications line. However, such a splice may only be required for a single or a limited number of fibers within the monotube. Under such circumstances, it is extremely time consuming and degrading to the communication efficiency to completely severe and subsequently splice all the optical fibers in a monotube in order to access a single optical fiber. It is, therefore, advantageous to utilize a device which allows access to a limited number of fibers within the monotube without cutting or otherwise disturbing the remaining optical fibers.
Presently, there are various optical fiber access tools for use with monotube design optical fiber cables. For instance, AT&T Western Electric manufactures Unit Slitter Tool (961B or 961C) for accessing the optical fibers within a monotube. However, before the Unit Slitter Tool can be used, all of the monotube cable's protective elements, such as the polyethylene outer jacket, the strength members, the corrugated armor jacket and the radial strength yarns, must be removed in order to provide access to the monotube.
Another optical fiber access tool is manufactured by Alcatel Cable Systems and is described in U.S. patent application Ser. No. 07/713,749, filed June 11, 1991 under the title Monotube Cable Fiber Access Tool, now U.S. Pat. No. 5,140,751, . In using this tool, it is also necessary to remove all of the protective elements of the monotube cable, with the exception of the longitudinally extending strength members, in order to utilize the tool for accessing the optical fibers within the monotube.
At present, in order to provide access to the buffer tube within the monotube optical fiber cable so the previously described tools can be used, various methods and tools have been utilized to strip away the outer cable components including the jacket, rigid strength members and steel corrugated shield. For instance, one current method requires at least six items: (1) razor blades (for cutting the outer jacket); (2) needle-nose pliers (for removing the outer jacket and corrugated shield); (3) a small screwdriver (for peeling back the corrugated shield); (4) a pair of wire cutters (for severing the rigid strength members); (5) a pair of tin snips (for cutting the corrugated shield); and (6) scissors (for cutting the radial strength yarns and the rip cord). This procedure requires a substantial amount of time (at least eight minutes) for an experienced operator. In addition, it is potentially hazardous to the operator because of the sharp tools involved which require proficient handling in order to avoid injury to the user. The potential danger of loose razor blades, wire cutters and scissors in a busy work environment such as in the field is great.
In addition, due to the filling compounds used, such as the petroleum-based hot melt filling compound or the hot melt adhesive, the above-referenced procedure is quite messy and sticky because of the compound that is encountered when removing the protective elements.
Also, oftentimes, it is desirable to leave the strength members intact for providing additional cable support thereby creating even more difficulty in accessing the buffer tube. For instance, the strength members are left intact when the previously mentioned Alcatel fiber access tool is used. When the strength members are not severed, it is quite difficult to remove all of the monotube cable's protective elements, i.e., the corrugated armor jacket and the radial strength yarns as the positioning of the strength members make it difficult to manipulate the screwdriver, the scissors and the tin snips as required.
As can clearly be seen, providing an optical fiber cable cutter for use with a monotube optical fiber cable for accessing the central buffer tube is a difficult problem which has not been previously resolved. Even with the current level of understanding of optical fiber cables, there has not previously been a practicable optical fiber cable cutter which can sever all necessary cable components in a single operation to obtain buffer tube access although such a tool would be desirable.